Because the scale isn't binary here - you don't have only a) people who blindly trust doctors, and b) people who are conspiracy nuts.

Both of them are wrong, btw. Pharma companies are greedy and they do everything they can to make you spend more. Doctors are influenced by them, often very subtly. That is a fact, not a conspiracy. But the fact also is, that doctors save lives and most have noble intentions (despite the meat grinder medical career is). One needs to learn what information belongs more to "greedy companies" category, and what belongs to "life saving science" category. It's no surprise people get confused about this - and that's why you absolutely need to explain to them why they need to finish antibiotics treatments.